Field of the Invention
The present invention relates to a vibration-type driving apparatus that brings a vibrator and a driven body into pressure contact with each other and moves the vibrator and the driven body relatively to each other by exciting vibrations in the vibrator, and in particular to a drive control circuit which drives the vibrator and a method to drive the vibrator.
Description of the Related Art
There is known a vibration-type actuator which brings a driven body into pressure contact with a vibrator, which is constructed by joining an electro-mechanical energy conversion element to an elastic body, and excites a predetermined vibration in the vibrator by applying an alternating-current signal to the electro-mechanical energy conversion element to thus move the vibrator and the driven body relatively to each other.
For example, there is known a vibrator in which a piezoelectric element, which is an electro-mechanical energy conversion element, is bonded to a first side of a plate-like elastic body, and two projecting portions are provided with a predetermined spacing therebetween on a second side opposite to the first side (see Japanese Laid-Open Patent Publication (Kokai) No. 2009-89586). In this vibrator, elliptical motion is produced in the projecting portions in a plane including a direction that connects the two projecting portions and a direction of a plate thickness of the elastic body by applying voltage to the piezoelectric element. By bringing the driven body into pressure contact with upper sides of the two projecting portions, the two projecting portions are caused to give driving force to the driven body in a driving direction that connects the two projecting portions together.
In this vibration-type actuator, while the vibrator is not being driven, the positional relationship between the vibrator and the driven body is held unchanged by frictional force, and hence there is no need to have an additional mechanism that keeps positions of the vibrator and the driven body. This enables downsizing, weight-saving, structure simplification, and so forth of various apparatuses having the vibration-type actuator.
In the vibration-type actuator described above, however, holding force generated between the vibrator and the driven body by pressure contact is influenced by moisture, humidity environment, and so forth between surfaces of contact, and when there is moisture between frictional sliding surfaces of the vibrator and the driven body, holding force decreases. For this reason, particularly when a long time period has elapsed after operation of the vibrator was stopped or when the vibrator and the driven body are used in a high-humidity environment, the vibrator and the driven body may become misaligned when the driving direction is switched or when the driven body is subjected to external force.